GPU: Only allow the UI channel to preempt if all stubs are scheduled.

gpu/command_buffer/service/gpu_scheduler.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_GPU_SCHEDULER_H_
 #define GPU_COMMAND_BUFFER_SERVICE_GPU_SCHEDULER_H_
 
 #include <queue>
 
 #include "base/atomicops.h"
@@ skipping 62 matching lines @@
   // Returns whether the scheduler is currently able to process more commands.
   bool IsScheduled();
 
   // Returns whether the scheduler needs to be polled again in the future.
   bool HasMoreWork();
 
   // Sets a callback that is invoked just before scheduler is rescheduled.
   // Takes ownership of callback object.
   void SetScheduledCallback(const base::Closure& scheduled_callback);
 
+  // Sets a callback that is invoked just before scheduler is descheduled.
+  // Takes ownership of callback object.
+  void SetDescheduledCallback(const base::Closure& descheduled_callback);
+
   // Implementation of CommandBufferEngine.
   virtual Buffer GetSharedMemoryBuffer(int32 shm_id) OVERRIDE;
   virtual void set_token(int32 token) OVERRIDE;
   virtual bool SetGetBuffer(int32 transfer_buffer_id) OVERRIDE;
   virtual bool SetGetOffset(int32 offset) OVERRIDE;
   virtual int32 GetGetOffset() OVERRIDE;
 
   void SetCommandProcessedCallback(const base::Closure& callback);
 
   void DeferToFence(base::Closure task);
@@ skipping 47 matching lines @@
   struct UnscheduleFence {
     UnscheduleFence(gfx::GLFence* fence, base::Closure task);
     ~UnscheduleFence();
 
     scoped_ptr<gfx::GLFence> fence;
     base::Closure task;
   };
   std::queue<linked_ptr<UnscheduleFence> > unschedule_fences_;
 
   base::Closure scheduled_callback_;
+  base::Closure descheduled_callback_;
   base::Closure command_processed_callback_;
 
   // If non-NULL and |preemption_flag_->IsSet()|, exit PutChanged early.
   scoped_refptr<PreemptionFlag> preemption_flag_;
   bool was_preempted_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuScheduler);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_GPU_SCHEDULER_H_